This invention relates to measurement devices using a light beam to measure distance to an object and, in particular, simultaneous multi-point measurement devices using a single laser source.
Head suspensions are well known and commonly used within dynamic magnetic or optical information storage devices or drives with rigid disks. The head suspension is a component within the disk drive that positions a magnetic or optical read/write head over a desired position on the storage media where information is to be retrieved (read) or transferred (written). Head suspensions for use in rigid disk drives typically include a load beam that generates a spring force and that supports a flexure to which a head slider having a read/write head is to be mounted. The load beam includes a mounting region at a proximal end, a rigid region at a distal end, and a spring region between the rigid region and the mounting region for providing the spring force. The spring region of each load beam is rolled or otherwise bent in such a manner as to plastically bend or deform the spring region, thereby imparting a curved shape to the spring region and causing the flexure to be offset from the mounting region in a z-height direction when the suspension is in its unloaded or free state.
Head suspensions are normally combined with an actuator arm or E-block to which the mounting region of the load beam is mounted with a base plate so as to position (by linear or rotary movement) the head suspension, and thus the head slider and read/write head, with respect to data tracks of the rigid disk. The rigid disk within a disk drive rapidly spins about an axis, and the head slider is aerodynamically designed to xe2x80x9cflyxe2x80x9d on an air bearing generated by the spinning disk. The spring force (often referred to as the xe2x80x9cgram loadxe2x80x9d) generated by the load beam urges the head slider in a direction opposing the force generated by the air bearing. The point at which these two forces are balanced during operation is the xe2x80x9cfly heightxe2x80x9d of the head slider.
The flexure typically includes a slider bond pad to which a head slider is attached. The flexure attached to the load beam provides a resilient connection between the slider and the load beam, and permits pitch and roll motion of the head slider and read/write head as they move over the data tracks of the disk in response to fluctuations in the air bearing caused by fluctuations in the surface of the rigid disk. Head suspension flexures can be provided in numerous ways, including designs in which the load beam and flexure are formed integrally with one another (a two-piece design comprising the base plate and the integral load beam/flexure) and designs in which the flexure is a separate piece from the load beam (a three-piece design comprising the base plate, the load beam and the separate flexure). One three-piece design includes a flexure having a resilient tongue and two resilient spring arms. The head slider is supported on the resilient tongue (i.e. the slider bond pad), which is in turn supported between the spring arms. The spring arms are connected to a flexure mounting region, which is in turn connected to the load beam. The gram load provided by the spring region of the load beam is transferred to the flexure via a dimple that extends between the rigid region of the load beam and the flexure. The spring arms allow the tongue of the flexure to gimbal in pitch and roll directions to accommodate surface variations in the spinning magnetic disk over which the slider is flying. The roll axis about which the head slider gimbals is a central longitudinal axis of the head suspension. The pitch axis about which the head slider gimbals is perpendicular to the roll axis. That is, the pitch axis is transverse to the longitudinal axis of the load beam, and crosses the roll axis at or around the head slider.
In order to store and retrieve data from magnetic or optical disks on which data is densely packed, it is necessary for the head slider to fly closely above the surface of the spinning data disk (on the order of 0.1 xcexcm) without colliding with the disk (xe2x80x9ccrashingxe2x80x9d). Further, because of the dense packing of data on magnetic or optical disks, it is important for the read/write head attached to the head slider to be able to read from or write to a relatively small area or spot on the disk.
One performance-related criteria of a suspension is specified in terms of its resonance characteristics. In order for the head slider assembly to be accurately positioned with respect to a desired track on the magnetic disk., the suspension must be capable of precisely translating or transferring the motion of the positioning arm to the slider assembly. An inherent property of moving mechanical systems, however, is their tendency to bend and twist in a number of different modes when driven back and forth at certain rates known as resonant frequencies. Any such bending or twisting of a suspension causes the position of the head slider assembly to deviate from its intended position with respect to the desired track. Since the head suspension assemblies must be driven at high rates of speed in high performance disk drives, the resonant frequencies of a suspension should be as high as possible.
The position, shape and size of the roll or bend in the spring region of a suspension, sometimes generally referred to as the radius geometry or profile of the suspension, can greatly affect its resonance characteristics. The radius geometry of a suspension must therefore be accurately controlled during manufacture to optimize the resonance characteristics of the part. The radius geometry of a suspension may be characterized by different parameters. By way of example, Hutchinson Technology Incorporated, the assignee of the present application, has often characterized the radius geometry of suspensions using a number of parameters including those referred to as xe2x80x9cheight,xe2x80x9d and xe2x80x9cdepthxe2x80x9d or xe2x80x9crippel.xe2x80x9d
A radius geometry related z-height is often measured using a laser triangulation probe, also known as a point range sensor. Optical point range sensors are generally known and commercially available from a number of suppliers, including WYKO Corporation of Tucson, Ariz. The point range sensor produces a focused or converging beam of light which is directed at a known angle to a point to be measured on the surface of the suspension or other target. An image of the spot of light produced on the target is projected onto a detector. The position of the image of the light spot on the detector will vary as a function of the distance between the instrument and the measurement target, i.e., the suspension. The position of the image of the light spot on the detector can then be correlated by triangulation to a z-height measurement. The point range sensor may provide a height parameter measurement of the suspension when the suspension is in various configurations, such as when the suspension is in a rest position or when it is elevated to the fly height. Laser triangulation offers relatively fast point readings with measurements in less than 1 millisecond, and can offer relatively good distance accuracy.
The currently preferred location on the suspension for measuring the radius geometry related z-height, hereinafter referred to as RG height, is in the spring region. Preferably, two measurements are taken, one on either side of spring region. In order to provide both measurements, the point range sensor must be mounted on a movable stage or other movable device, or the suspension must be mounted on a movable device. A triangulated height measurement is then taken on a first side of the spring region by the point range sensor. The sensor and suspension are then moved relative to one another, such as by movement of the sensor on the movable stage, and a second height measurement is taken on a second side. These two height measurements may then be averaged and the difference between the two measurements, known hereinafter as the Delta height, is then also calculated.
Although measurement of z-height at a point on a target by a point range sensor, as described above, is relatively accurate, the need to move the sensor and/or the target to obtain a second z-height reading causes errors and inaccuracies to occur in the averaged RG height and Delta height measurements. These errors are mainly due to actuation of the movable stage by a motor, which in turn produces heat that causes distortion of the stage and sensor or suspension mounting structure. It has been measured that the temperature increase in the mounting structure can cause as much as a 7 micrometer difference in a height measurement that is only about xc2x120 micrometers. In addition, the need to measure two points and move the sensor between measurements causes a cycle time delay that may be about 100 milliseconds.
The current need within the head suspension industry for ever smaller and more accurate suspensions has produced a corresponding need for more accurate measurements. There is also a continuing need to develop more efficient methods for correcting head suspension parameters without significant impact on other performance criteria of the head suspension for which accurate measurements would be useful.
A measurement device in accordance with the present invention overcomes the shortcomings of presently available measurement devices by providing the ability to measure multiple points on a target simultaneously, quickly and accurately using a single light source, such as a laser. The measurement device may include a laser for producing a laser light beam and optics that split the laser beam into a plurality of differentiable beam portions, such as a plurality of polarized beams. The optics also direct the differentiable beam portions toward the target to be measured producing light spots on the target. The measurement device also includes a detection component, such as a plurality of position sensing detectors, positioned to intercept the images of the light spots on the target projected towards the detectors. Additional beam reflecting and directing elements may also be included to facilitate detection of the images of the light spots.
The data collected by the detection component may be used to calculate measurement data related to the target. When used with a head suspension target, displacement of various regions of the head suspension may be measured relative to a reference region, such as the mounting region of the head suspension. In particular the target region on the head suspension may include the spring region and, from the displacement measurements, RG height and Delta height values may be determined. The present invention measurement device maybe incorporated into a head suspension production system, thus allowing for rapid adjustment of characteristic parameters of the head suspension during production.